(1) Field of the Invention
The present invention relates to a phonograph pickup arm for use with disc records and more particularly to an improved pickup arm arranged and constructed so as to maintain the stylus in contact with the recorded surface and compensate for error in the tracking path.
(2) Description of the Prior Art
In the recording of phonograph records, the recording is performed in such a manner that the recording cutter head usually moves linearly across the disc to be recorded. At the same time it is common practice in modern phonograph record players to mount the pickup on an arm that is pivoted at some point beyond the rim of the phonograph turntable. These arms while providing very little friction suffer from the unfortunate effect, in their simplest forms to be unable to eliminate the resulting tracking error between the pickup and record groove. This discrepancy gives rise to tracking distortion as well as providing undesirable pressure on the sides of the stylus included in the phonograph pickup. The simplest approach to solving this particular problem is the utilization of an offset arm which reduces the noted tracking errors but does not eliminate them and increases side pressure on the stylus. Obviously it is impossible to reproduce the sounds on the record disc with the degree of fidelity desired because of said so called tracking errors. To compensate for the tracking error it is required to maintain the cartridge carrying the stylus in a direction tangential to the sound groove of the recorded disc throughout the record playing.
Several differenct techniques have been suggested to eliminate the tracking error. One conventional method for that purpose involves attaching the base end of the pickup arm to spiral advancing means which are arranged over or outside of the turntable arm, to laterally move the base end of the pickup arm; and to thus carry the stylus in the direction of the diameter of the recorded disc. Thus the track of the stylus is positioned through the center of the record and obviously eliminates any tracking errors, since the reproduced tracking path essentially follows the initial recording path. In addition to extreme complexity and cost such arrangements suffer from other problems such as stiffness of the included electrical leads and friction. One pickup arm of this type which overcomes some of the problems but essentially is still a complex and expensive form of pickup arm is disclosed in U.S. Pat. No. 2,915,315 which issued on Dec. 1, 1959 to Jacob Rabinow.
Another conventional method for the prevention or elimination of tracking error is disclosed in U.S. Pat. No. 3,476,394, which teaches the mounting of a transducer on a transducer arm which in turn is carried on a slave arm mounted for rotational movement parallel with the plane of the disc with the transducer arm being allowed to move in relation to the slave arm about an axis normal to the plane of the disc. Drive means are included which move the pickup arm in or out upon the slave arm as the slave arm rotates about its normal axis thus changing the effective length of the transducer arm whereby as the pickup stylus moves across the face of the disc it lies in a plane approximating that of the original recording stylus. This system too, is a complex and expensive system requiring a separate drive means to effectively change the length of the transducer arm combination to effect the improved operation.
A similar pickup arm assembly for eliminating tracking error is disclosed in U.S. Pat. No. 3,924,860. In the disclosed arrangement, detecting means are included for detecting whether a fixed point lies on the fulcrum of the line connecting the pickup arm and the stylus and control means, for controlling a rotary member supporting the pickup arm to operate in cooperation with the detecting means to compensate for the normally present tracking error.
All of the techniques for eliminating tracking errors represented by the above noted patents suffer from the drawback of the extreme complexity and resultant expense. Accordingly it is the object of the present invention to provide a novel phonograph pickup arm which elements the above mentioned disadvantages.